Fixed #17277 - Wrap IOErrors raised due to client disconnect in a specific...

Fixed #17277 - Wrap IOErrors raised due to client disconnect in a specific IOError subclass so they can be distinguished from more serious errors. Thanks David Lowe.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17493 bcc190cf-cafb-0310-a4f2-bffc1f526a37